1. Field of the Invention
This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method for semiconductor fabrication supervision and optimization.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the operating speed of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate dielectric thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the FET, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors.
Additionally, reducing the size, or scale, of the components of a typical transistor also increases the density, and number, of the transistors that can be produced on a given amount of wafer real estate, lowering the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
However, reducing the size, or scale, of the components of a typical transistor also requires being able to form and pattern components such as the gate conductor and gate dielectric on such reduced scales, consistently, robustly and reproducibly, preferably in a self-aligned manner. Moreover, reducing the channel length of a transistor also requires reducing the size and area of electrical contacts to active areas, such as N+ (P+) source/drain regions and a doped-polycrystalline silicon (doped-polysilicon or doped-poly) gate conductor. As the size and area of the electrical contacts to the active areas get smaller, the active area contact resistance increases. Increased active area contact resistance is undesirable for a number of reasons. For example, increased active area contact resistance may reduce device drive current, and source/drain current through the device, and may also adversely affect the overall speed and operation of the transistor.
Typically, depositing titanium (Ti) or cobalt (Co) on the active area electrical contacts may decrease active area contact resistance. The cobalt (Co) may then be silicided by annealing with a heat-treatment to form cobalt silicide (CoSi2) at the active area electrical contacts (self-aligned silicidation or salicidation). The salicided CoSi2 lowers active area contact resistance.
As shown in FIG. 1, a metal oxide semiconductor field effect transistor (MOSFET or MOS transistor) 100 may be formed on a semiconducting substrate 105, such as doped-silicon. The MOS transistor 100 may have a doped-poly gate 115 formed above a gate dielectric 110 formed above the semiconducting substrate 105. The doped-poly gate 115 and the gate dielectric 110 may be separated from N+-doped (P+-doped) source/drain regions 120 of the MOS transistor 100 by dielectric spacers 125. The dielectric spacers 125 may be formed above Nxe2x88x92-doped (Pxe2x88x92-doped) source drain extension (SDE) regions 130.
The Nxe2x88x92-doped (Pxe2x88x92-doped) source drain extension (SDE) regions 130 are typically provided to reduce the magnitude of the maximum channel electric field found close to the N+-doped (P+-doped) source/drain regions 120 of the MOS transistor 100, and, thereby, to reduce the associated hot-carrier effects. The lower (or lighter) doping of the Nxe2x88x92-doped (Pxe2x88x92-doped) source drain extension (SDE) regions 130, relative to the N+-doped (P+-doped) source/drain regions 120 of the MOS transistor 100, reduces the magnitude of the maximum channel electric field found close to the N+-doped (P+-doped) source/drain regions 120 of the MOS transistor 100, but increases the source-to-drain resistances of the Nxe2x88x92-doped (Pxe2x88x92-doped) source drain extension (SDE) regions 130.
As shown in FIG. 2, a cobalt (Co) metal layer 235 may be blanket-deposited on the MOS transistor 100 shown in FIG. 1, following a pre-cleaning dip performed to remove residual dielectric material from areas to be salicided. The cobalt (Co) metal layer 235 may then be subjected to an initial rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 450-800xc2x0 C. for a time ranging from approximately 15-60 seconds. At surfaces 240 of active areas 245, such as the N+-doped (P+-doped) source/drain regions 120 and the doped-poly gate 115, exposed silicon (Si) reacts upon heating with the cobalt (Co) metal layer 235 to form cobalt silicide (CoSi2) at the surfaces 240 of the active areas 245. The cobalt (Co) metal layer 235 is not believed to react with the dielectric spacers 125 upon heating.
As shown in FIG. 3, a wet chemical strip of the cobalt (Co) metal layer 235 removes excess, unreacted portions (not shown) of the cobalt (Co) metal layer 235, leaving behind the salicided cobalt silicide (CoSi2) 350 only at and below the surfaces 240 of the active areas 245. The salicided cobalt silicide (CoSi2) 350 may then be subjected to a final rapid thermal anneal (RTA) process performed at a temperature ranging from approximately 600-1000xc2x0 C. for a time ranging from approximately 10-60 seconds.
Unsalicided resistors have found many applications in complementary metal oxide silicon (CMOS) semiconductor technology. For example, a layer of polysilicon disposed in a semiconducting substrate may form a portion of a resistor. However, unless protected by an overlying salicide block, the layer of polysilicon disposed in the semiconducting substrate would become silicided during a subsequent salicidation process, as described above. The silicidation of the layer of polysilicon would render the resistor much less resistive. Consequently, a conventional salicide block formed of a single layer of silicon dioxide (SiO2) or tetraortho silicate (TEOS) is typically formed above such a resistor. However, in the formation of conventional salicide blocks, there is little selectivity to field oxide and/or silicon (Si) during the salicide block etch, performed to form the salicide block. Since an overetch is typically performed (to ensure substantially complete removal of extraneous salicide block material for increased salicidation in other areas of the workpiece), the silicon (Si) loss and/or the field oxide loss can be very significant, particularly in silicon-on-insulator (SOI) applications. In silicon-on-insulator (SOI) applications, the silicon (Si) film and/or the field oxide thickness are much less than in xe2x80x9cbulkxe2x80x9d applications.
Conventional semiconductor devices may be referred to as xe2x80x9cbulkxe2x80x9d devices, because bulk devices include a substantially monocrystalline semiconducting bulk substrate in which the active and/or passive circuit elements are disposed. More recently, silicon-on-insulator (SOI) devices have been introduced that consume less power than do bulk devices, an important advantage in many applications such as battery-powered mobile telephones and battery-powered laptop computers. Also, silicon-on-insulator (SOI) devices advantageously operate at higher speeds than do bulk devices.
Silicon-on-insulator (SOI) devices may be characterized by having a thin layer of insulating dielectric material (for example, a buried oxide or nitride or other suitable insulating layer) sandwiched between a bulk semiconducting substrate and the circuit elements of the device. Typically, no other layers of material are interposed between the buried dielectric layer and the bulk substrate. As used herein, the circuit elements establish a circuit component, such as an active transistor or a passive component (e.g., resistor).
In a silicon-on-insulator (SOI) device, the circuit elements above the buried dielectric layer are established in regions of a thin film of substantially monocrystalline semiconducting layer, often bonded and/or grown epitaxially, that are separated from each other by insulating dielectric regions (of field oxide, for example). The (epitaxial) semiconducting layer may be n-doped or p-doped as appropriate with N-type or P-type conductivity dopants. For example, the (epitaxial) semiconducting layer may include a body region having a P-type dopant, the body region being disposed between source/drain regions. The source/drain regions may be doped with an N-type dopant. Such a structure may be used to form an N-channel metal oxide silicon field effect transistor (MOSFET or MOS transistor) or a lateral NPN bipolar transistor, for example.
The silicon-on-insulator (SOI) technology offers a number of advantages relative to traditional transistor formation in a bulk silicon wafer. For example, bulk silicon transistors have their active terminals disposed adjacent the bulk silicon wafer. As a result, parasitic capacitance is present at the junction between the source/drain regions of an MOS transistor and the well or bulk silicon substrate. Other problems with bulk silicon transistors include the possibility of junction breakdown between the source/drain regions and the wafer, together with the formation of undesired parasitic bipolar transistors giving rise to device latch-up problems.
In contrast, silicon-on-insulator (SOI) transistors have active regions (for example, the source/drain and channel regions of an MOS transistor) formed adjacent an underlying insulating layer. As such, these silicon-on-insulator (SOI) transistors protect against and/or significantly reduce the formation of undesired parasitic elements. The silicon-on-insulator (SOI) technology also significantly reduces junction capacitance and junction leakage due to the reduced exposed junction area. This reduced parasitic capacitance leads to increased performance and higher density integrated circuits. Also, silicon-on-insulator (SOI) transistors offer inherent radiation hardness, better high temperature performance, higher current driving ability, and lower leakage current.
One disadvantage with silicon-on-insulator (SOI) devices is that the voltage in the body region of the device tends to vary, or xe2x80x9cfloat.xe2x80x9d This is sometimes referred to as a floating body. Consequences of floating body silicon-on-insulator (SOI) devices include output current kinks, anomalous subthreshold currents, transient current overshoot, and early device breakdown.
Silicon-on-insulator (SOI) techniques offer, however, additional advantages. In some cases, it uses simpler fabrication sequences and resultant cross-sections compared to circuits fabricated in bulk silicon. Silicon-on-insulator (SOI) techniques also provide reduced capacitive coupling between various circuit elements over the entire integrated circuit (IC) chip, and, in CMOS circuits, latchup is substantially reduced. Silicon-on-insulator (SOI) techniques reduce chip size and/or increase packing density, and minimum device separation is determined only by the limitations of photolithography. Moreover, silicon-on-insulator (SOI) techniques provide increased circuit speed, due in part to reductions in parasitic capacitance and chip size.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a method is provided, the method comprising forming a buffer layer above a structure layer, and forming a dielectric layer above the buffer layer. The method also comprises patterning the dielectric layer to form a salicide block above a portion of the structure layer protecting the portion from a subsequent salicidation.
In another aspect of the present invention, a device is provided, the device comprising a buffer layer above a structure layer and a dielectric layer above the buffer layer. The dielectric layer is patterned to form a salicide block above a portion of the structure layer to protect the portion from a subsequent salicidation.